1. Field of the Invention
The present invention relates to an image pickup apparatus that performs white balance control and a method of controlling the same, and more particularly to white balance processing performed by the image pickup apparatus.
2. Description of the Related Art
In recent years, in automatic white balance processing performed by an image pickup apparatus, a so-called TTL (Through The Lens) method is widely used. In automatic white balance processing using the TTL method, the color of light from a light source is estimated according to an image obtained by photographing. Further, to calculate a white balance correction value (hereinafter referred to as a WB correction value), it is necessary to accurately distinguish, on the image, between the color of light from the light source and the color of the object.
For example, there has been proposed an image pickup apparatus that is configured to change a white change range for determining an evaluation value of a color signal according to a photographing condition and an object condition, to thereby perform accurate color temperature detection and white balance control, in a manner independent of a luminance signal level (see Japanese Patent Laid-Open Publication No. H11-262029).
Further, there has been proposed an image pickup apparatus that is configured to perform proper white balance control with respect to a green object included in a white extraction range, on which an action for converting green to an achromatic color works (e.g. in a case where green trees or grasses are photographed in a dark place, such as a place in the shade) (see Japanese Patent Laid-Open Publication No. 2006-174281). In this image pickup apparatus, white balance is controlled by determining, based on distribution of data on a three-dimensional coordinate system having an illuminance, an amount of green, and an R gain, as coordinate axes, whether an image has been photographed indoors using indoor fluorescent lamps as a light source, or has been photographed outdoors in the sun/shade.
Now, let it be assumed that the color of light from a light source itself, such as a mercury lamp, is green, and a scene is photographed in which a whole image obtained by photographing is made greenish by the light (first scene). Further, let it be assumed that a scene in which there are a lot of green trees or grasses (second scene) are photographed in a dark place, such as a place in the shade. In such cases, it is difficult for the image pickup apparatuses, described in Japanese Patent Laid-Open Publication No. H11-262029 and Japanese Patent Laid-Open Publication No. 2006-174281, to discriminate between the first scene and the second scene.
That is, in the image pickup apparatus described in Japanese Patent Laid-Open Publication No. H11-262029, the first scene and the second scene both have similar evaluation values of the brightness and the color of the object between the two scenes, and hence there is a high possibility that the WB correction values for the first scene and the second scene are also similar to each other.
Further, also in the image pickup apparatus described in Japanese Patent Laid-Open Publication No. 2006-174281, the whole image is made greenish due to the influence of the color of light from the light source, and hence even with the use of the amount of green and the R gain, it is difficult to discriminate between the first scene and the second scene.
It is desirable that the green colored by the light from the light source in the first scene is converted to an achromatic color, but it is desirable that the green of the object in the second scene is made brilliant. Therefore, it is desirable to discriminate between the first scene and the second scene, and change the WB correction value according to the scene.